The process of splitting away a portion of a concrete masonry unit to provide a decorative "rockface" to the finished unit is well-known. In the case where the finished rockface is planar, it has not been uncommon to provide a linear splitting groove or pattern on the uppermost surface of the pre-split unit to aid in the splitting process.
Anchor Wall Systems, Inc. ("AWS"), my assignee, forms a faceted or "three-way" split face on some of its concrete retaining wall units. The process first requires that a pre-split concrete masonry unit be formed by a block machine. The pre-split unit must be larger than the finished unit, so that a portion of it can be split away to form the decorative face. If the block machine is large enough, the pre-split unit comprises what will ultimately be two retaining wall blocks, joined face-to-face. Otherwise, the pre-split unit comprises the finished unit with a sacrificial portion joined to its face. Some of the AWS retaining wall units, such as the ANCHOR WINDSOR STONE.RTM., ANCHOR DIAMOND.RTM., and DIAMOND PRO.TM., are formed with lips to facilitate the locating of the blocks in a wall. Since the block machine forms the units on flat, horizontal metal pallets, the pre-split units are cast with the lips facing up.
After a pre-split unit is formed in the block machine, it is hardened by any one of a variety of curing techniques, until it has attained a suitable hardness for splitting. It is then split in a splitting machine. The unit is carried into the splitting station on a roller conveyor. It is supported there by a divided receiving plate. The splitting is typically accomplished with a top knife, which is driven down onto the pre-split unit, in combination with an opposed bottom knife and opposed side knives.
In the case of the three-way split, the top and bottom knives are formed in the shape of a "crow's foot", comprising a straight center section joining two diverging V-shaped portions. Up until now, AWS has molded vertical splitting grooves, which define the rearward edges of the return facets on the finished units, into the sides of the pre-split units. The side knives engage these grooves during the splitting process.
Heretofore, AWS has not formed any type of splitting groove or pattern into the top surface of a pre-split unit which is to be split to form faceted faces on the finished units, and, in particular, has not formed any such patterns by the compressive action of a stripper shoe plate carrying appropriate tooling.
I have noted several shortcomings of the current system. It is difficult to create a face with an extended straight section and relatively short returns, particularly on the taller products. For example, AWS' current ANCHOR WINDSOR STONE.RTM. product is a four inch high block, twelve inches wide. The center section of the face is eight inches wide and the return sections are each two inches wide in front projection. AWS' current ANCHOR DIAMOND.RTM. product is a six inch high block. The center section of the face is eight inches wide and the return sections are each four inches wide in front projection. AWS has not experienced unusual difficulty in splitting these faces to the stated proportions if side knives are employed in combination with a top knife. However, AWS would like to increase the length of the center section of the ANCHOR DIAMOND.RTM. block to twelve inches, with approximately two inch returns (front projections). AWS has experienced difficulty in consistently splitting off such small wedges from the six inch tall product with standard automated splitting equipment. If the return splits are not acceptable, then the blocks must be manually dressed to make them acceptable, which increases the labor costs.
AWS would also like to minimize the need to use side knives, especially during the splitting of the ANCHOR WINDSOR STONE.RTM. product. This is because elimination of the side knives would permit the manufacturer to position two pre-split units in the splitter side-by-side, and thus create four split units with one stroke of the splitter.
Another problem is that as the block gets taller, it gets more difficult to get good return splits, regardless of how long the wedge is. For example, AWS' DIAMOND PRO.TM. blocks are eight inch tall products. The center section of the face of each is twelve inches wide, and the returns are three inches wide in front projection. It is difficult to consistently split the three inch wide returns on these products using conventional equipment and techniques.